Modern agricultural implements for sowing seed or distributing other products such as fertilizers and chemicals typically have one or more row units for distributing product in rows in a field as the implement is moved over the field. Various types of implements are known, including, but not limited to planters, drills, air seeders and nutrient applicators. Such machines are referred to herein generally as a product distribution apparatus or machine. When the distributed product is placed under the soil surface, a furrow opener is used to open a furrow into which the product is deposited. The furrow is then closed, covering the product. A typically opener is a single or double disc opener having one or two discs oriented at a slight angle to the forward direction of travel. A depth regulation member is positioned near the opener to limit the penetration of the opener into the soil to produce a furrow of the desired depth.
A downward force is needed for the opener to penetrate the soil to the desire depth. When the opener is fully penetrating the soil, the depth regulating member, often in the form of a “gauge wheel,” contacts the soil surface. The physical weight of the row unit together with the weight of any product stored on the row unit provides a downward force to help the opener penetrate the soil. However, this weight is often insufficient to ensure full penetration of the opener. It has long been the practice to provide supplemental down force to the row unit in the form of a mechanical spring arrangement. Such spring arrangements are adjustable so the operator can select a desired amount of supplemental down force before operating the implement. Changes in the amount of down force during operation is not possible.
More recently, the mechanical springs have been replaced with hydraulic or pneumatic actuators that allow the operator to make changes to the down force during machine operation. Changes are made through a control system that adjusts the hydraulic or pneumatic pressure delivered to each actuator. Even more recently, active or dynamic control of the down force is accomplished with a load sensor to measure to the soil reaction force on the depth regulation member. With dynamic control of the down force, a control system automatically operates the down force actuators by changing the system pressure in response to changing soil conditions in the field as the machine is moved over a field to achieve a desired soil reaction force on the depth regulation member.
Such active control systems can produce wide variations in the hydraulic or pneumatic pressures of the down force system as the machine moves through a field. A high capacity air compressor or hydraulic pump is needed to achieve the variation in a reasonable time. A high capacity system adds considerably to the overall cost. Large variations in the system pressures can be reduced by turning off the dynamic control of the down force for certain areas the field.